Method of manufacturing nitride semiconductor light-emitting element

ABSTRACT

A method of manufacturing a nitride semiconductor light-emitting element includes: growing an n-side superlattice layer that includes InGaN layers and GaN layers; and, after the step of growing the n-side superlattice layer, growing a light-emitting layer. The step of growing the n-side superlattice layer comprises repeating a cycle n times (n is a number of repetition), the cycle including growing one InGaN layer and growing one GaN layer. In the step of growing the n-side superlattice layer, the step of growing one GaN layer in each cycle from a first cycle to an mth cycle is performed using carrier gas that contains N2 gas and does not contain H2 gas. The step of growing one GaN layer in each cycle from a (m+1)th cycle to an nth cycle is performed using gas containing H2 gas as the carrier gas.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims priority to Japanese Patent Application No.2017-019717, filed on Feb. 6, 2017, the disclosure of which is herebyincorporated by reference in its entirety.

BACKGROUND

The present disclosure relates to a method of manufacturing a nitridesemiconductor light-emitting element.

In recent years, semiconductor light-emitting elements, such aslight-emitting diodes, have been used for a wide variety ofapplications, including various types of illumination devices.Accordingly, such light emitting elements are required to emit lightwith a high brightness at a low drive voltage. To meet such arequirement, for example, JP 2016-92253 A discloses a method formanufacturing a light-emitting element that can emit light with a highbrightness. In JP 2016-92253 A, a method of manufacturing a nitridesemiconductor light-emitting element is described in which an n-sidelayer includes an n-side superlattice layer. In a step of forming then-side superlattice layer, an InGaN layer, a GaN layer on the InGaNlayer, and an n-type GaN layer on the GaN layer are repeatedly formed.When forming the InGaN layer, nitrogen gas is used as the carrier gas .When forming the n-type GaN layer, a mixed gas in which nitrogen gas andhydrogen gas are mixed is used as the carrier gas.

SUMMARY

In the light-emitting element manufactured by using the method describedin JP 2016-92253 A, it is possible to improve brightness to some extent,but forward voltage Vf tends to be increased.

Accordingly, it is an object of certain embodiments of the presentdisclosure to provide a method of manufacturing a nitride semiconductorlight-emitting element in which the brightness thereof can be improvedwhile reducing an increase in the forward voltage Vf.

According to one embodiment, a method of manufacturing a nitridesemiconductor light-emitting element includes: growing an n-sidesuperlattice layer that includes InGaN layers and GaN layers; and, afterthe step of growing the n-side superlattice layer, growing alight-emitting layer. The step of growing the n-side superlattice layercomprises repeating a cycle n times (n is a number of repetition), thecycle including growing one InGaN layer and growing one GaN layer. Inthe step of growing the n-side superlattice layer, the step of growingone GaN layer in each cycle from a first cycle to an mth cycle isperformed using carrier gas that contains N₂ gas and does not contain H₂gas. The step of growing one GaN layer in each cycle from a (m+1)thcycle to an nth cycle is performed using gas containing H₂ gas as thecarrier gas.

The method of manufacturing a nitride semiconductor light-emittingelement according to certain embodiments described herein can produce anitride semiconductor light-emitting element which improves thebrightness while reducing an increase in the forward voltage Vf.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-sectional view showing the structure of alight-emitting element according to one embodiment.

DETAILED DESCRIPTION

Nitride semiconductor light-emitting elements according to certainembodiments will be described below with reference to the accompanyingdrawing.

A nitride semiconductor light-emitting element 100 according to the oneembodiment includes: a substrate 1; an underlayer 2 on the substrate; ann-side contact layer 3; an n-side superlattice layer 4; an active layer5; a p-side cladding layer 6; and a p-side contact layer 7, which arelayered in this order from the side of the substrate 1. The n-sidesuperlattice layer 4 includes n pairs of InGaN layers and GaN layers,each pair including a single InGaN layer and a single GaN layer.Hereinafter, the “pairs of InGaN layers and GaN layers, each pairincluding a single InGaN layer and a single GaN layer” may be referredto simply as “pairs”. In the n-side superlattice layer 4, GaN layers 4a, each of which is the single GaN layer, in each of m pairs of the npairs from the underlayer 2 side, are grown using N₂ gas, which does notcontain hydrogen, as the carrier gas. The GaN layers 4 x, each of whichis the single GaN layer in each pair from the (m+1)th pair to the nthpair of then pairs, i.e., at the active layer 5 side, are grown usinggas, which contains H₂ gas, as the carrier gas. In the n-sidesuperlattice layer 4, preferably, InGaN layers 4 b, each of which is thesingle GaN layer in each of k pairs of the n pairs from the underlayer 2side, are undoped layers not doped with n-type impurities. Preferably,the InGaN layers 4 s, each of which is the single GaN layer in each pairfrom the (k+1)th pair to the nth pair of the n pairs, are layerscontaining n-type impurities. As shown in FIG. 1, in the n-sidesuperlattice layer 4, for example, the layer closest to the underlayer 2is the GaN layer 4 a, and the layer closest to the active layer 5 is theInGaN layer 4 s. The active layer 5 formed on the n-side superlatticelayer 4 includes well layers and barrier layers that are alternatelyformed. For example, the active layer 5 is disposed on the n-sidesuperlattice layer 4 such that the barrier layer included in the activelayer is in contact with the InGaN layer 4 s disposed closest to theactive layer 5 in the n-side superlattice layer 4. The p-side claddinglayer 6 and the p-side contact layer 7 are formed in this order on theactive layer 5. As used herein, “n” is an integer greater than 2, “m” isan integer greater than 0 and smaller than n, and “k” is an integergreater than 0 and smaller than n. The expression “from the (m+1) thpair to the nth pair” as used herein, includes the case of m=n−1, i.e. ,the expression “from the (m+1) th pair to the nth pair” may indicateonly the nth pair, that is, the pair closest to the active layer 5. Theexpression “from the (k+1) th pair to the nth pair” as used hereinincludes the case of k=n−1, i.e. , the expression “from the (k+1) thpair to the nth pair” may indicate only the nth pair, that is, the pairclosest to the active layer 5.

A p-electrode 9 is disposed on a part of the surface of the p-sidecontact layer 7. An n-electrode 8 is disposed on a surface (i.e.,electrode formation surface) of the n-side contact layer 3 exposed byremoving a portion of each of the p-side contact layer 7, the p-sidecladding layer 6, and the active layer 5, in a predetermined region.

Examples of nitride semiconductors in the nitride semiconductorlight-emitting element according to the present embodiment include groupIII-V nitride semiconductors (In_(x)Al_(y)Ga_(1-x-y)N (0≤X, 0≤Y, X+Y≤1). The group III-V nitride semiconductor may be a mixed crystal in whichB is used for a part of the group III element, or P, As, or Sb issubstituted for a part of N of the group V element. Such a nitridesemiconductor layer can be formed, for example, by metal-organicchemical vapor deposition (MOCVD),hydridevaporphaseepitaxy(HVPE),molecular beam epitaxy (MBE), or thelike.

In the nitride semiconductor light-emitting element with theconfiguration mentioned above, an active layer with better crystallinitycan be formed; thus an emission output can be increased and an increasein the forward voltage Vf can be reduced or prevented. These effects canbe greatly exhibited in the nitride semiconductor light-emitting elementin which the active layer 5 includes a well layer containing arelatively large amount of In and which has an emission peak wavelengthof 500 nm or greater (for example, the light emitting element configuredto emit green light and includes the well layer made of InGaN in whichan In content is approximately 20.0 to 25.0%). The expression “A-B”,where “A” and “B” are numbers, as used herein refers to a range of A toB in which A and B is included.

A description will be given below of respective components of thenitride semiconductor light-emitting element obtained by a method ofmanufacturing according to the present embodiment.

Substrate 1

An insulating substrate made of, for example, sapphire or spinel(MgAl₂O₄) in which any one of the C plane, the R plane, and the A planeis a main surface can be used as the substrate 1 on which asemiconductor layer is to be formed. Among these, the sapphire substrateis preferable. Examples of a material suitable for the substrate 1 mayinclude SiC (examples thereof including 6H, 4H, and 3C), ZnS, ZnO, GaAs,and Si. The substrate 1 may or may not be removed at the end ofmanufacturing.

n-Side Contact Layer 3

The n-side contact layer 3 contains n-type impurities in at least a partthereof and serves to supply and diffuse carriers in the electrodeformation surface and into a light-emitting layer. In particular, inorder to supply the carriers from the n-electrode 8 toward the activelayer 5 through in-plane diffusion, the n-side contact layer 3 ispreferably doped with n-type impurities at a relatively highlyconcentration. The n-side contact layer 3 is preferably made of GaN.

n-Side Superlattice Layer 4

The n-side superlattice layer 4 is disposed to improve the crystallinityof the active layer 5 and the like formed thereon. As described above,the n-side superlattice layer includes n pairs of InGaN layers and GaNlayers, each pair including a single InGaN layer and a single GaN layer.The “n” represents the number of the pairs, and is, for example, in arange of 10 to 40, preferably 15 to 35, and more preferably 25 to 35.For example, a nitride semiconductor light-emitting element configuredto emit blue light, where the In content in a well layer of the activelayer 5 is relatively small, includes 20 pairs of the InGaN layers andthe GaN layers. A nitride semiconductor light-emitting elementconfigured to emit green light, where the In content in the well layerof the active layer 5 is relatively large, includes 30 pairs of theInGaN layers and the GaN layers. Each of the GaN layers 4 a and 4 xpreferably has a thickness of 1.5 nm to 5 nm, and more preferably 2 nmto 4 nm. Each of the InGaN layers 4 b and 4 s preferably has a thicknessof 0.5 nm to 3 nm, and more preferably 0.7 nm to 2 nm. The thicknessesof the GaN layers 4 a and 4 x and the InGaN layers 4 b and 4 s maydiffer among the pairs. For example, the thickness of the GaN layer 4 aon the n-side contact layer 3 side may differ from the thickness of theGaN layer 4 x on the active layer 5 side. Likewise, the thickness of theInGaN layer 4 b on the n-side contact layer 3 side may differ from thethickness of the InGaN layer 4 s on the active layer 5 side.

As described above, in the n-side superlattice layer 4, the GaN layers 4a in m pairs from the underlayer 2 side are grown using N₂ gas, whichdoes not contain hydrogen, as the carrier gas, and the GaN layers 4 x inpairs from the (m+1) th pair to the nth pair, that is, on the activelayer 5 side are grown using gas, which contains H₂ gas, as the carriergas. The number of pairs of InGaN layers and GaN layers grown on theactive layer 5 side using gas containing H₂ gas as the carrier gas isexpresses as (n−m) , and is preferably in a range of 1 to 5, morepreferably 2 to 4, and even more preferably 2 or 3. With the number of(n−m), which indicates the number of pairs of InGaN layers and GaNlayers grown on the active layer 5 side using gas containing H₂ gas asthe carrier gas, of 1 or greater, a surface of the GaN layer 4 a is lesslikely to have a large recess (i.e. , V-shaped pit) , and thus can bemore flat, and the crystallinity of the GaN layers 4 a can be improved.Consequently, the active layer 5 can be formed favorably on the uppersurface of the GaN layer 4 a. It is considered that growing the GaNlayer 4 a while supplying gas containing H₂ gas as the carrier gasallows the growth in the lateral direction of the GaN layer 4 a to beaccelerated, which allows for preventing increase in size of the recessformed on the surface of the GaN layer 4 a, so that a large recess isnot easily formed in the surface of the GaN layer 4 a. With the numberof (n−m) , which indicates the number of the pairs on the active layer 5side grown by using gas containing H₂ gas as the carrier gas, of 5 orless, the brightness of the light-emitting element can be improvedwithout excessively increasing the forward voltage Vf.

In contrast, in the n-side superlattice layer 4, if the GaN layers 4 ain several pairs from the underlayer 2 side, not from the active layer 5side, are grown using gas containing H₂ gas as the carrier gas, thebrightness is hardly improved, and the forward voltage Vf tends toincrease. This is considered to be due to that, in the n-sidesuperlattice layer 4, improvement in a surface state of the GaN layer 4a on the underlayer 2 a side does not allow a surface of the GaN layer 4a on which the active layer 5 is to be formed to be a flat surface, sothat the active layer 5 is not efficiently formed.

As described above, in the n-side superlattice layer 4, preferably, theInGaN layers 4 b in the k pairs from the underlayer 2 side are undopedlayers, i.e., not doped with n-type impurities, whereas the InGaN layers4 s in pairs from the (k+1) th pair to the nth pair are layerscontaining n-type impurities. The number of pairs on the active layer 5side that include the InGaN layers 4 s containing n-type impurities isindicated by (n−k), and is preferably in a range of 2 to 5, and morepreferably 3 or 4. With the number of (n−k), which indicates the numberof pairs on the active layer 5 side that include the InGaN layers 4 scontaining n-type impurities, of 2 or more, the effect of reducing theforward voltage Vf by containing n-type impurities in the superlatticelayer can be efficiently obtained, and an increase in the forwardvoltage Vf can be prevented. Further, with the number of (n−k), whichindicates the number of pairs on the side of the active layer 5 thatinclude the InGaN layers 4 s containing n-type impurities, of 5 or less,deterioration of the superlattice layer due to the contained n-typeimpurities can be prevented, while reducing or preventing an increase inthe forward voltage Vf, so that electrostatic resistance can bemaintained.

In the n-side superlattice layer 4, if the InGaN layers 4 b in severalpairs from the side of the underlayer 2, not from the active layer 5side, contain n-type impurities, electrostatic resistance of the lightemitting element can be improved, but its forward voltage Vf andbrightness tends to deteriorate. This is considered to occur because nolayer that contains n-type impurities is formed on the active layer 5side in the n-side superlattice layer 4, and thus carriers are lesslikely to be injected into the active layer 5.

The n-type impurity concentration of the InGaN layers 4 s from the(k+1)th pair to the nth is preferably in a range of 1×10¹⁸/cm³ to5×10¹⁸/cm³, and more preferably 2×10¹⁸/cm³ to 4×10¹⁸/cm³.

Further, in the n-side superlattice layer 4, the number of (n−k), whichindicates the number of pairs on the active layer 5 side that includethe InGaN layers 4 s containing the n-type impurities, is preferablylarger than the number of (n-m), which indicates the number of pairs onthe active layer 5 side that include the GaN layers grown by using gascontaining H₂ gas as the carrier gas.

In the nitride semiconductor light-emitting element containing then-side superlattice layer with the structure described above, thecrystallinity of the active layer 5 can be improved, and the in-planecurrent diffusion when driven can be enhanced, so that its electrostaticresistance can be improved. Therefore, in the nitride semiconductorlight-emitting element according to the present embodiment, brightnesscan be improved without increasing the forward voltage Vf, and theelectrostatic resistance characteristics can be maintained.

Active Layer 5

A nitride semiconductor containing In is preferably used for the activelayer 5. With the appropriate proportion of In, the nitridesemiconductor light-emitting element can emit the light in the range ofultraviolet region to the visible light (red light) region, and can alsoachieve high luminous efficiency. For example, when the well layer ismade of In_(x)Ga_(1-x)N, the In composition x is selected so as toobtain a desired emission color. The emission wavelength of the nitridesemiconductor light-emitting element is selected such that a peakemission peak wavelength is in a range of 430 nm to 570 nm, preferably500 nm to 570 nm. The barrier layer can be made of, for example, GaN,InGaN, AlGaN, or the like. The well layer and the barrier layer maycontain n-type impurities such as Si, and/or p-type impurities such asMg, or otherwise may be undoped.

p-Side Cladding Layer 6

The p-side cladding layer 6 served to confine carriers therein. Forexample, the p-side cladding layer 6 can be made of GaN, AlGaN, or thelike that contains p-type impurities such as Mg. The p-side claddinglayer 6 has a thickness of 10 nm to 30 nm, for example.

p-Side Contact Layer 7

The p-side contact layer 7 is a layer having an upper surface on whichan electrode is formed. For example, the p-side contact layer 7 can bemade of GaN, AlGaN, or the like that contains p-type impurities such asMg. The p-side contact layer 7 has a thickness of 100 nm to 150 nm, forexample.

A method of manufacturing the nitride semiconductor light-emittingelement according to the present embodiment will be described below.

Forming Underlayer

The underlayer 2 is formed, for example, on a C-plane of the substrate 1made of sapphire by the metal-organic chemical vapor deposition (MOCVD)via a buffer layer.

The buffer layer is formed, for example, by growing AlGaN on thesubstrate using raw material gas, such as trimethylaluminum (TMA),trimethylgallium (TMG), or ammonia, at a low temperature of 600° C. orlower.

The underlayer 2 is formed, for example, by growing GaN on the bufferlayer using TMG and ammonia as the raw material gas. The underlayer 2maybe formed to be multiple layers that include, for example, a firstlayer grown at 1050° C. and a second layer grown at 1,150° C.

Forming n-Side Contact Layer

Then, the n-side contact layer 3 is formed, for example, by growing ann-type GaN, which contains n-type impurities made of Si, on theunderlayer 2 at a temperature of 1,150° C. using TMG and ammonia as theraw material gas and using monosilane as n-type impurity gas.

Forming n-Side Superlattice Layer

Then, the n-side superlattice layer 4 is formed, for example, byalternately growing a GaN layer an InGaN layer at 860° C., which islower than the temperature at which the n-side contact layer 3 is grown.

Regarding each pair, when growing the GaN layer, in the first cycle tothe mth cycle for formation of the m pairs from the n-side contact layer3 side, the GaN layer is grown using triethylene glycol (TEG) andammonia as the raw material gas and N₂ gas as the carrier gas, whereasin the (m+1)th cycle to the nth cycle (i.e., final cycle) for formationof the (n-m) pairs on the active layer 5 side, the GaN layer is grownusing TEG and ammonia as the raw material gas and H₂ gas as the carriergas. It is preferable that only H₂ gas is used as the carrier gas usedfor growing the GaN layer in the (m+1)th cycle to the nth cycle. Usingonly H₂ gas allows for easily obtaining the above-mentioned effects,such as suppressing an increase in size of a V-shaped pit at the GaNlayer 4 a. The expression “the (m+1)th cycle to the nth cycle” as usedherein includes the case of m=n−1, i.e. , the case where “the (m+1)thcycle to the nth cycle” indicated only the final cycle.

Regarding each pair, when growing the InGaN layer, in the first cycle tothe kth cycle for formation of the k pairs from the n-side contact layer3 side, the InGaN layer 4 b is grown using TEG, TMI, and ammonia as theraw material gas and N₂ gas as the carrier gas without supplying anyn-type impurity gas, whereas in the (k+1)th cycle to the nth cycle(final cycle) for formation of the (n−k) pairs on the side of the activelayer 5, the InGaN layer 4 s is grown using TEG, TMI, and ammonia as theraw material gas to which the n-type impurity gas supplied and N₂ gas asthe carrier gas. At the time of growing the InGaN layers 4 b and 4 s,the concentration of the n-type impurity gas is set such that the Inproportion in each of the InGaN layers 4 b and 4 s is preferably in arange of 1% to 10% and more preferably 1% to 3%. The term “the (k+1)thcycle to the nth cycle” as used herein includes the case of k=n−1, i.e.,the case where “the (k+1)th cycle to the nth cycle” indicates only thefinal cycle.

Forming Active Layer 5

Then, for example, a barrier layer made of GaN is grown on the n-sidesuperlattice layer 4 at a temperature of 950° C., and subsequently awell layer made of InGaN is grown on the barrier layer at a temperatureof 800° C., by using TEG, TMI, and/or ammonia as the raw material gas.

These barrier and well layers are alternately grown, and finally thebarrier layer made of GaN is grown, so that the active layer 5 isformed.Forming p-Side Cladding Layer 6

Then, the p-side cladding layer 6 is formed, for example, by growingp-type AlGaN that contains p-type impurities of Mg on the active layer 5by using TEG and ammonia as the raw material gas and using Cp₂Mg(cyclopentadienyl magnesium) as p-type impurity gas.

Forming p-Side Contact Layer 7)

Subsequently, for example, an undoped GaN layer is grown on the p-sidecladding layer 7 by using TMG, TMA, and ammonia as the raw material gas.Then, p-type GaN containing p-type impurities of Mg is grown on theundoped GaN layer by using TMG, TMA, and ammonia as the raw material gasand Cp₂Mg (cyclopentadienyl magnesium) as the p-type impurity gas, sothat the p-side contact layer 7 is formed. The concentration ofimpurities in the p-side contact layer 7 is preferably higher than thatin the p-side cladding layer 6.

After the growth, a wafer is placed in a reactor vessel under a nitrogenatmosphere and subjected to annealing at a temperature of about 700° C.,which is lower than the temperature at which the above-mentionedrespective layers are grown, so that the resistance of each of thep-side cladding layer 6 and the p-side contact layer 7 can be reduced.

After the annealing, a portion of each of the p-side contact layer 7,the p-side cladding layer 6, and the active layer 5 in the certainregion are removed to expose the surface (electrode formation surface)for forming the n-electrode 8.

Then, the p-electrode 9 and the n-electrode 8 are formed on the part ofthe surface of the p-side contact layer 7 and on the electrode formationsurface, respectively.

Through the steps described above, the nitride semiconductorlight-emitting element is manufactured.

Examples of the present invention will be described below.

EXAMPLES Example 1

A nitride semiconductor light-emitting element was manufactured by amethod of manufacturing as described below.

Substrate 1

A substrate made of sapphire was used as the substrate 1. A sapphire(C-plane) for growing a nitride semiconductor was cleaned at atemperature of 1,050° C. under a hydrogen atmosphere in a metal organicchemical vapor deposition (MOCVD) reactor vessel.

Buffer Layer

A buffer layer made of AlGaN, was grown on the substrate at atemperature of 550° C. to have a thickness of approximately 12 nm, usingTMA, TMG, and ammonia as the raw material gas.

Underlayer 2

GaN was grown to have a thickness of appropriately 1 μm on the bufferlayer at a temperature of 1, 050° C. using TMG and ammonia as the rawmaterial gas. Subsequently, on this layer, GaN was further grown to havea thickness of appropriately 1 μm at a temperature of 1,150° C. usingTMG and ammonia as the raw material gas. The two GaN layers grown inthis way is collectively referred to as the “underlayer 2”.

n-Side Contact Layer 3

Then, an n-side contact layer 3 made of n-type GaN doped with Si at adensity of 1×10¹⁹ atoms/cm³ was grown to have a thickness of 6 μm on theunderlayer 2 at a temperature of 1,150° C. using TMG, ammonia, andmonosilane.

n-Side Superlattice Layer 4

Then, at a temperature of 860° C., an n-side superlattice layer 4 wasformed by repeating a cycle of growing a GaN layer and an InGaN layer 30times, as described below.

A GaN layer 4 a was grown to have a thickness of 3 nm on the n-sidecontact layer using TEG and ammonia as the raw material gas and using N₂gas as the carrier gas (step A1). It is noted that in Example 1, thedescription in which only a single kind of gas is used as the carriergas indicates that the carrier gas consists of substantially only thesingle kind of gas, and substantially no other kinds of gas arecontained in the carrier gas. That is, in the step A1, the carrier gasconsists of substantially only N₂ gas. Then, an InGaN layer 4 b wasgrown to have a thickness of 1 nm on the GaN layer using TEG, TMI, andammonia as the raw material gas and using N₂ gas as the carrier gas(step B1).

A combination of the step A1 and the step B1 was taken as one cycle, andthe cycle was repeated 27 times, i.e., from the first cycle to thetwenty-seventh cycle.

In the twenty-eighth cycle, a GaN layer 4 x was grown to have athickness of 3 nm using TEG and ammonia as the raw material gas andusing H₂ gas as the carrier gas (step A2). At this time, the flow rateof H₂ gas was set at 80 slm. In Example 1, in order to control the flowof a mixed gas composed of raw material gas and carrier gas at thegrowth surface of the substrate when growing the respective layers,control gas composed of N₂ gas was caused to flow from the obliquelyupper side with respect to the growth surface of the substrate.Consequently, within the MOCVD reactor vessel, the raw material gas, thecarrier gas, and the control gas are allowed to coexist. Meanwhile, thecarrier gas containing the raw material gas was mainly blown on thegrowth surface of the substrate, and the control gas was not mainlybrown thereto. Thus, even in the case where the control gas made of N₂is used, the growth of the GaN layer 4 x can be controlled as long as H₂is used as the carrier gas. In the step A2 of Example 1, the flow rateof H₂ gas as the carrier gas was set at 80 slm, and the flow rate of N₂gas as the control gas was set at 150 slm. That is, the ratio of theflow rate of H₂ gas to the total flow rate of H₂ gas and N₂ gas was setat approximately 35%.

Next, an InGaN layer 4 s doped with Si at a density of 3×10¹⁸ atoms/cm³was grown on the GaN layer using TEG, TMI, and ammonia as the rawmaterial gas, monosilane as the n-type impurity gas, and N₂ gas as thecarrier gas (step B2).

A combination of the step A2 and the step B2 was taken as one cycle, andthe cycle was repeated 3 times, i.e., from the twenty-eighth cycle tothe thirtieth cycle.

In the manner as described above, the superlattice layer including 30GaN layers and 30 InGaN layers were formed. That is, the n-sidesuperlattice layer 4 was formed where n was 30 and each of m and k was27.

Active Layer 5

Next, a GaN layer doped with Si at a density of 4×10¹⁸ atoms/cm³ wasgrown to have a thickness of 6 nm, on the superlattice layer at atemperature of 930° C. using TEG, TMI, and ammonia as the raw materialgas and using monosilane as the n-type impurity gas, and subsequently anundoped GaN layer was grown to have a thickness of 3 nm on the doped GaNlayer. Further, a well layer made of In_(0.25)Ga_(0.75)N and a barrierlayer made of GaN, which were taken as one pair, were alternately grownon the undoped GaN layer to obtain nine pairs. Specifically, each welllayer was grown at a temperature of 800° C. to have a thickness of 3 nmusing TEG, TMI, and ammonia as the raw material gas, and each barrierlayer was grown at a temperature of 960° C. to have a thickness of 19 nmusing TEG and ammonia as the raw material gas. In addition, on the ninepairs of the well layers and the barrier layers, a well layer made ofIn_(0.25)Ga_(0.75)N and a barrier layer made of GaN, which were taken asone pair, were alternately grown to obtain three pairs. Specifically,each well layer was grown at a temperature of 800° C. using TEG, TMI,and ammonia as the raw material gas to have a thickness of 3 nm, andeach barrier layer was grown at a temperature of 960° C. using TEG andammonia as the raw material gas to have a thickness of 16 nm. In thismanner, the active layer 5 was formed.

p-Side Cladding Layer 6

Then, a p-side cladding layer 6, made of Al_(0.13)Ga_(0.87)N doped withMg at a density of 2×10²⁰ atoms/cm³, was formed to have a thickness of11 nm on the active layer 5 at a temperature of 930° C. using TEG, TMA,and ammonia as the raw material gas and Cp₂Mg (cyclopentadienylmagnesium) as the p-type impurity gas.

p-Side Contact Layer 7

Subsequently, a p-type contact layer 7 was formed by, at a temperaturebetween approximately 850° C. and 1000° C., growing an undoped GaN layeron the p-side cladding layer and a doped p-type GaN layer doped with Mgat a density of 5×10²⁰ atoms/cm³ on the undoped GaN layer. Specifically,the undoped GaN layer was grown to have a thickness of approximately 80nm using TMG and ammonia, and the doped p-type GaN layer was grown tohave a thickness of approximately 40 nm using TMG, ammonia, and Cp₂Mg.

After the growth, the substrate 1 with the nitride semiconductor formedthereon was subjected to annealing in a reactor vessel under a nitrogenatmosphere at a temperature of about 700° C., so that the resistance ofeach of the p-side cladding layer 6 and the p-side contact layer 7 isreduced.

After the annealing, a portion of each of the p-side contact layer 7,p-side cladding layer 6, and active layer 5 in the certain region wereremoved to expose the surface for forming the n-electrode 8 (i.e.,electrode formation surface).

Then, the p-electrode 9 and the n-electrode 8 were formed on a portionof the surface of the p-side contact layer 7 and on the electrodeformation surface, respectively.

In the nitride semiconductor light-emitting element of Example 1manufactured in a manner as described above, the forward voltage Vfrequired to allow the forward current of 65 mA to flow therethrough was3.30 V, and VL was 107.31. An average peak emission wavelength was 532.9nm. As used herein, “VL” is an index representing the brightness of thenitride semiconductor light-emitting element, and the larger this valueVL, the greater the brightness of the nitride semiconductorlight-emitting element is, and the smaller the value VL, the smaller thebrightness of the nitride semiconductor light-emitting element is. Inthe Example 1, VL was determined by allowing the electric current toflow between the p-electrode and the n-electrode of the nitridesemiconductor light-emitting element formed on the substrate 1 using aprober, causing the nitride semiconductor light-emitting element to emitlight, receiving the emitted light with a photodiode, and measuring. TheVL value as used herein is an average value of VL values measured in aplurality of nitride semiconductor light-emitting elements formed on thesubstrate 1.

Example 2

A nitride semiconductor light-emitting element in Example 2 wasmanufactured in the same manner as in Example 1 except that the n-sidesuperlattice layer 4 was formed in the manner as below.

n-Side Superlattice Layer 4

In Example 2, the step A1 was performed in each cycle from the firstcycle to the twenty-sixth cycle, and the step B1 was performed in eachcycle from the first cycle to the twenty-seventh cycle. Further, thestep A2 was performed in each cycle from the twenty-seventh cycle to thethirtieth cycle, and the step B2 was performed in each cycle from thetwenty-eighth cycle to the thirtieth cycle. That is, the n-sidesuperlattice layer 4 was formed where n was 30, m was 26, and k was 27.

In the nitride semiconductor light-emitting element of Example 2,manufactured in the manner as described above, the forward voltage Vfrequired to allow the forward current of 65 mA to flow therethrough was3.38 V, and VL was 106.97. An average peak emission wavelength was 531.6nm.

Example 3

A nitride semiconductor light-emitting element in Example 3 wasmanufactured in the same manner as in Example 1 except for the n-sidesuperlattice layer 4 formed as below.

n-Side Superlattice Layer 4

In Example 3, the step A1 was performed in each cycle from the firstcycle to the twenty-fifth cycle, and the step B1 was performed in eachcycle from the first cycle to the twenty-seventh cycle. Further, thestep A2 was performed in each cycle from the twenty-sixth cycle to thethirtieth cycle, and the step B2 was performed in each cycle from thetwenty-eighth cycle to the thirtieth cycle. That is, the n-sidesuperlattice layer 4 was formed where n was 30, m was 25, and k was 27.

In the nitride semiconductor light-emitting element of Example 3,manufactured in the manner as described above, the forward voltage Vfrequired to allow the forward current of 65 mA to flow therethrough was3.49 V, and VL was 109.52. An average peak emission wavelength was 532.2nm.

Example 4

A nitride semiconductor light-emitting element in Example 4 wasmanufactured in the same manner as in Example 1 except that the n-sidesuperlattice layer 4 was formed in the following way.

n-Side Superlattice Layer 4

In Example 4, the step A1 was performed in each cycle from the firstcycle to the twenty-eighth cycle, and the step B1 was performed in eachcycle from the first cycle to the twenty-seventh cycle. Further, thestep A2 was performed in each cycle from the twenty-ninth cycle to thethirtieth cycle, and the step B2 was performed in each cycle from thetwenty-eighth to the thirtieth cycles. That is, the n-side superlatticelayer 4 was formed where n was 30, m was 28, and k was 27.

In the nitride semiconductor light-emitting element of Example 4,manufactured in the manner as described above, the forward voltage Vfrequired to allow the forward current of 65 mA to flow therethrough was3.28 V, and VL was 105.53. An average emission peak wavelength was 530.3nm.

Example 5

A nitride semiconductor light-emitting element in Example 5 wasmanufactured in the same manner as in Example 1 except for that then-side superlattice layer 4 formed in the manner as described below.

n-Side Superlattice Layer 4

In Example 5, the step A1 was performed in each cycle from the firstcycle to the twenty-ninth cycle, and the step B1 was performed in eachcycle from the first cycle to the twenty-seventh cycle. Further, thestep A2 was performed in the thirtieth cycle, and the step B2 wasperformed in each cycle from the twenty-eighth to the thirtieth cycles.That is, the n-side superlattice layer 4 was formed where n was 30, mwas 29, and k was 27.

In the nitride semiconductor light-emitting element of Example 5,manufactured in the manner as described above, the forward voltage Vfrequired to allow the forward current of 65 mA to flow therethrough was3.26 V, and VL was 102.95. An average peak emission wavelength was 529.5nm.

Example 6

A nitride semiconductor light-emitting element in Example 6 wasmanufactured in the same manner as in Example 1 except for that then-side superlattice layer 4 was formed as described below.

n-Side Superlattice Layer 4

In Example 6, the step B2 was performed in each cycle from the firstcycle to the twenty-seventh cycle, and the step B1 was performed in eachcycle from the first cycle to the twenty-eighth cycle. Further, the stepA2 was performed in each cycle from the twenty-eighth cycle to thethirtieth cycle, and the step B2 was performed in each cycle from thetwenty-ninth to the thirtieth cycle. That is, the n-side superlatticelayer 4 was formed where n was 30, m was 27, and k was 28.

In the nitride semiconductor light-emitting element of Example 6,manufactured in the manner as described above, the forward voltage Vfrequired to allow the forward current of 65 mA to flow therethrough was3.37 V, and VL was 106.92. An average peak emission wavelength was 528.1nm.

Example 7

A nitride semiconductor light-emitting element in Example 7 wasmanufactured in the same manner as in Example 1 except that the n-sidesuperlattice layer 4 was formed as described below.

n-Side Superlattice Layer 4

In Example 7, the step A1 was performed in each cycle from the firstcycle to the twenty-seventh cycle, and the step B1 was performed in eachcycle from the first cycle to the twenty-sixth cycle. Further, the stepA2 was performed in each cycle from the twenty-eighth cycle to thethirtieth cycle, and the step B2 was performed in each cycle from thetwenty-seventh to the thirtieth cycles. That is, the n-side superlatticelayer 4 was formed where n was 30, m was 27, and k was 26.

In the nitride semiconductor light-emitting element of Example 7,manufactured as described above, the forward voltage Vf required toallow the forward current of 65 mA to flow therethrough was 3.30 V, andVL was 108.46. An average peak emission wavelength was 528.8 nm.

Example 8

A nitride semiconductor light-emitting element in Example 8 wasmanufactured in the same manner as in Example 1 except that the n-sidesuperlattice layer 4 was formed as below.

n-Side Superlattice Layer 4

In Example 8, the step A1 was performed in each cycle from the firstcycle to the twenty-seventh cycle, and the step B1 was performed in eachcycle from the first cycle to the twenty-fifth cycle. Further, the stepA2 was performed in each cycle from the twenty-eighth cycle to thethirtieth cycle, and the step B2 was performed in each step from thetwenty-sixth cycle to the thirtieth cycle. That is, the n-sidesuperlattice layer 4 was formed where n was 30, m was 27, and k was 25.

In the nitride semiconductor light-emitting element of Example 2,manufactured as described above, the forward voltage Vf required toallow the forward current of 65 mA to flow therethrough was 3.29 V, andVL was 109.75. An average peak emission wavelength was 527.1 nm.

Example 9:

A nitride semiconductor light-emitting element in Example 9 wasmanufactured in the same manner as in Example 1 except that the n-sidesuperlattice layer 4 formed as below.n-Side Superlattice Layer 4

In Example 9, the step A1 was performed in each cycle from the firstcycle to the twenty-seventh cycle, and the step B1 was performed in eachcycle from the first cycle to the thirtieth cycle. Further, the step A2was performed in each step from the twenty-eighth cycle to the thirtiethcycle. That is, the n-side superlattice layer 4 was formed where n was30, m was 27, and k was 30.

In the nitride semiconductor light-emitting element of Example 9,manufactured in the manner as described above, the forward voltage Vfrequired to allow the forward current of 65 mA to flow therethrough was3.68 V, and VL was 107.30. An average peak emission wavelength was 530.3nm.

Comparative Example 1

A nitride semiconductor light-emitting element in Comparative Examplewas manufactured in the same manner as in Example 1 except that ann-side superlattice layer was formed as below.

n-Side Superlattice Layer 4

In Comparative Example 1, the step A1 was performed in each cycle fromthe first cycle to the thirtieth cycles, and the step B1 was performedin each cycle from the first cycle to the twenty-seventh cycle. Further,the step B2 was performed in each cycle from the twenty-eighth cycle tothe thirtieth cycle. That is, the n-side superlattice layer 4 was formedwhere n was 30, m was 30, and k was 27.

In the nitride semiconductor light-emitting element of ComparativeExample 1, manufactured in the manner as described above, the forwardvoltage Vf required to allow the forward current of 65 mA to flowtherethrough was 3.23 V, and VL was 97.60.

Table 1 shows the results of the structures and evaluation of the n-sidesuperlattice layers in Examples 1 to 9 and Comparative Example 1,described above.

TABLE 1 Number of GaN Number of growth layers InGaN layers in mixed gasdoped with Si (Number of (Number of Forward performing performingvoltage Brightness step A2) step B2) Vf VL Example 1 3 3 3.30 107.31Example 2 4 3 3.38 106.97 Example 3 5 3 3.49 109.52 Example 4 2 3 3.28105.53 Example 5 1 3 3.26 102.95 Example 6 3 2 3.37 106.92 Example 7 3 43.30 108.46 Example 8 3 5 3.29 109.75 Example 9 3 0 3.68 107.30Comparative 0 3 3.23 97.60 Example 1

From the results shown in Table 1, (1) and (2) as below can beunderstood.

-   (1) Growing the GaN layers on the active layer 5 side in the n-side    superlattice layer 4 using gas containing H₂ gas as the carrier gas    allows for improving the brightness (based on the comparison between    Examples 1 to 9 and Comparative Example 1).-   (2) Doping n-type impurities into the InGaN layer on the active    layer 5 side in the n-side superlattice layer 4 allows for reducing    the forward voltage Vf (based on the comparison between Examples 1    to 8 and Example 9).

As shown in Examples 1 to 9 as described above, according to the nitridesemiconductor light-emitting element of Examples 1 to 9, growing the GaNlayers on the active layer 5 side in the n-side superlattice layer 4using gas containing H₂ gas as the carrier gas allows for improvingbrightness of the light-emitting element. Further, doping n-typeimpurities into the InGaN layer on the active layer 5 side in the n-sidesuperlattice layer 4 allows for improving the brightness of thelight-emitting element and reducing the forward voltage Vf.

What is claimed is:
 1. A method of manufacturing a nitride semiconductorlight-emitting element, the method comprising: growing an n-sidesuperlattice layer that includes InGaN layers and GaN layers; and afterthe step of growing the n-side superlattice layer, growing alight-emitting layer, wherein: the step of growing the n-sidesuperlattice layer comprises: repeating a cycle n times (where n is anumber of repetitions), the cycle including: growing one InGaN layer,and growing one GaN layer, in the step of growing the n-sidesuperlattice layer, the step of growing one GaN layer in each cycle froma first cycle to a mth cycle is performed using carrier gas thatcontains N₂ gas and does not contain H₂ gas, and the step of growing oneGaN layer in each cycle from a (m+1) th cycle to an nth cycle isperformed using gas containing H₂ gas as the carrier gas.
 2. The methodof manufacturing a nitride semiconductor light-emitting elementaccording to claim 1, wherein: the step of growing the InGaN layer ineach cycle from the first cycle to a kth cycle is performed withoutsupplying an n-type impurity gas, and the step of growing the InGaNlayer in each cycle from (k+1)th cycle to the nth cycle is performedwhile supplying an n-type impurity gas.
 3. The method of manufacturing anitride semiconductor light-emitting element according to claim 1,wherein: a peak wavelength of the nitride semiconductor light-emittingelement is in a range of 500 nm to 570 nm.
 4. The method ofmanufacturing a nitride semiconductor light-emitting element accordingto claim 2, wherein: a peak wavelength of the nitride semiconductorlight-emitting element is in a range of 500 nm to 570 nm.
 5. The methodof manufacturing a nitride semiconductor light-emitting elementaccording to claim 1, wherein: n is in a range of 20 to
 40. 6. Themethod of manufacturing a nitride semiconductor light-emitting elementaccording to claim 2, wherein: n is in a range of 20 to
 40. 7. Themethod of manufacturing a nitride semiconductor light-emitting elementaccording to claim 5, wherein: (n−m), which indicates a number of cyclesfrom an (m+1)th cycle to the nth cycle, is in a range of 1 to
 4. 8. Themethod of manufacturing a nitride semiconductor light-emitting elementaccording to claim 6, wherein: (n−m), which indicates a number of cyclesfrom an (m+1)th cycle to the nth cycle, is in a range of 1 to
 4. 9. Themethod of manufacturing a nitride semiconductor light-emitting elementaccording to claim 5, wherein: (n−k) , which indicates a number ofcycles from (k+1) th cycle to the nth cycle, is in a range of 2 to 5.10. The method of manufacturing a nitride semiconductor light-emittingelement according to claim 6, wherein: (n−k) , which indicates a numberof cycles from (k+1) th cycle to the nth cycle, is in a range of 2 to 5.11. The method of manufacturing a nitride semiconductor light-emittingelement according to claim 7, wherein: (n−k) , which indicates a numberof cycles from (k+1) th cycle to the nth cycle, is in a range of 2 to 5.12. The method of manufacturing a nitride semiconductor light-emittingelement according to claim 8, wherein: (n−k) , which indicates a numberof cycles from (k+1) th cycle to the nth cycle, is in a range of 2 to 5.13. The method of manufacturing a nitride semiconductor light-emittingelement according to claim 1, wherein: m is greater than k.
 14. Themethod of manufacturing a nitride semiconductor light-emitting elementaccording to claim 2, wherein: m is greater than k.
 15. The method ofmanufacturing a nitride semiconductor light-emitting element accordingto claim 1, wherein: the GaN layer has a thickness of 1.5 nm to 5 nm.16. The method of manufacturing a nitride semiconductor light-emittingelement according to claim 2, wherein: the GaN layer has a thickness of1.5 nm to 5 nm.
 17. The method of manufacturing a nitride semiconductorlight-emitting element according to claim 1, wherein: the InGaN layerhas a thickness of 0.5 nm to 3 nm.
 18. The method of manufacturing anitride semiconductor light-emitting element according to claim 2,wherein: the InGaN layer has a thickness of 0.5 nm to 3 nm.